Emile Smith Rowe’s second half strike earned Arsenal a deserved three points in Mikel Arteta’s 100th game in charge.
The Englishman’s winner was his third goal from his last three games. He gave the Gunners the lead before Juraj Kucka was sent off for Watford late on.
Smith Rowe’s goal came days after he was left out of Gareth Southgate’s England squad for their upcoming World Cup qualifiers.
Captain Pierre-Emerick Aubameyang endured a wholly more frustrating day at the office, seeing a penalty saved and a goal ruled out for offside.
Arteta’s men are now on a 10-game unbeaten run stretching back to August – the longest such streak of the Spaniard’s tenure.
Watford battled valiantly with Claudio Ranieri having made five changes from the home defeat to Southampton – but they had Ben Foster in goal to thank for keeping them level for so long.
The experienced stopped saved his ninth Premier League penalty since 2010, with Aubameyang now missing his last two spot-kicks.
Arsenal thought they had hit the front early on, Watford giving the ball away on the edge of their own box before Bukayo Saka would eventually turn home – only for the England man to be called offside following a VAR check.
The game became scrappy with both sides picking up a couple of cautions, before Arsenal were awarded a penalty just after the half-hour.
Ainsley Maitland-Niles miscued a long-range effort which fell towards Alexandre Lacazette, who was clattered by Danny Rose.
Referee Kevin Friend pointed to the spot but Aubameyang’s penalty was brilliantly saved by Foster.
The incident seemed to spur on Watford, with Kucka having a shot blocked behind and Rose scuffing a strike from the resulting corner.
Arsenal were still creating chances of their own, Foster again in fine form to keep out a Gabriel Magalhaes header just before the break.
The Gunners would impose themselves on the game in the second half but were still unable to click as they have in recent weeks when attacking.
That was until Smith Rowe continued his fine run of form by opening the scoring after 56 minutes.
Benjamin White rode a number of challenges before being tackled, with the ball breaking into the path of Smith Rowe, who added to his goals against Aston Villa and Leicester by finishing well.
Aubameyang’s off-day continued when he slid in to convert substitute Martin Odegaard’s cross-cum-shot on the line, only to see the offside flag rule out the tap-in.
Odegaard gestured in frustration with replays showing his effort would have gone in without Aubameyang’s touch.
Watford had a glorious chance to level as White and Aaron Ramsdale left a clearance for one another and Joshua King stole in but opted to shoot from an acute angle, hitting the side netting of Arsenal’s empty goal.
The Hornets would be reduced to 10 men in the closing stages as Kukca was shown a second yellow card for catching Nuno Tavares in an attempt to clear the ball from the edge of the box.
Albert Sambi Lokonga stung the palms of Foster as Arsenal looked to put the game to bed in stoppage-time, seeing out the six additional minutes to seal another three points.